The present invention relates generally to methods and apparatus for measuring current or power delivered to loads in power distribution networks, and more specifically, to methods and apparatus for preventing overload conditions in power distribution equipment used to power equipment having variable input power requirements.
The proliferation of the Internet has created a need for large scale data centers that contain tens, if not hundreds, of racks of computing equipment, such as servers and routers. One of the major problems confronted by designers of these data centers is the requirement to route facility power to each of these racks of equipment. Typically, branch circuits from a primary or a secondary distribution panel are routed to groups of racks to provide power to the equipment in the rack. Each of the branch circuits is designed to provide a predetermined maximum power level or current, and the size of cabling used to route the power for a branch, and the size of circuit breakers used for the branch are selected based on this predetermined maximum power level or, more typically, predetermined maximum current.
Typically, it is desirable to design each of the branch circuits such that the total current drawn by the equipment coupled to any given one of the branch circuits is at some predetermined percentage (for example 50%) of the maximum current level for that branch circuit. This allows some flexibility to add additional equipment to racks and provides a safety margin below the maximum current level.
To properly design the routing of the branch circuits, it is desirable to know, with some accuracy, the current that is drawn by the equipment in the racks. Traditionally, the power or current drawn by computer equipment could be determined based on manufacturers"" specifications and/or by making actual measurements of the current being drawn by the equipment.
These measurements and specifications are only useful for equipment for which the current draw is substantially static, which in the past was true for typical computing equipment. However, for newer computing equipment, the current draw is typically not static due to a number of factors including: 1) many computers utilize some form of power management strategy which minimizes the power (and current) consumption of the computer by turning off or slowing down subsystems within the computer when they are not in use; 2) cooling systems (i.e., fans) are often speed controlled based on air and component temperatures to reduce power consumption and acoustic noise generation; and 3) the amount of power drawn by the processors and memory systems in computers has increased steadily with the increase of speed of the processors, so that the power consumed by the processors and memory subsystems may exceed 50% of the total power draw of a computer. The power drawn by processors and memory systems is variable depending on the processing load, and since the total power of these systems may be a significant portion of the total power, the total power draw of a computer can vary significantly depending on the processing load on the computer.
The operating systems of most computers are capable of simultaneously performing multiple tasks by assigning segments of the CPU processing time to each of the tasks on a priority basis. Any remaining segments of the CPU processing time are occupied by an idle task in which the CPU can be halted and all associated clocks can be stopped to reduce the power draw of the computer. Further, some computers, for example, those that utilize the Windows(copyright) 98 or Windows(copyright) 2000 operating system, have an Advanced Control and Power Interface (ACPI) feature that allows the operating system to control power to fans and other devices in the computer to further reduce the power drawn by the computer. Because of the factors described above, it is not unusual for a more modern system to consume twice as much power when the processors are fully computationally loaded and operating in a warm environment, then when computationally idle and operating in a cool environment.
The variability of the power draw of computers complicates the electrical design of data centers. Computer manufacturers typically provide power ratings on nameplates. These nameplate values are typically maximum values that are determined based on the maximum power that a computer may draw when fully loaded with all options and with all subsystems operating at full load. Because of conservative approaches taken in determining nameplate values, they are often greater than even worst case values for a given computer, and accordingly are of little use to an electrical facility designer. While a designer may measure the current drawn by a computer or a set of computers to determine the power draw, it is typically not known at the measurement time, whether the computer is at full load or at what percentage of full load the computer is operating.
Several problems may occur when circuit branches are designed based on measured power draw values of computers. First, the wiring used in power routing circuits may be undersized for full load conditions, and second, when one or more of the computers powered from a branch are operated at full load, the current drawn may exceed the circuit breaker value for the branch, causing the circuit breaker to trip and disconnect power to the computers. For critical applications of computers, any such power interruption is often unacceptable. Further, to prevent power interruptions to critical computers, it is common to use uninterruptible power supplies (UPSs) for these computers. Often, one UPS is used to power multiple computers or racks of computers. To properly size the UPS, it is necessary to know the power draw of each of the computers and other equipment powered by the UPS. The variability of the power draw in newer computers makes it difficult to properly size a UPS for these applications.
Embodiments of the present invention provide improved systems and methods for measuring the current or power draw of computers and racks of equipment that overcome problems described above.
A first aspect of the present invention is directed to a system for monitoring power in a power distribution system. The system includes a power monitoring device located in the power distribution system to measure a value of at least one characteristic of power provided to a branch of the power distribution system, the power monitoring device having an output that provides the value measured, and a controller having an input to receive the value measured and an output that couples to a first device powered by the branch of the power distribution system to send a power signal to the first device to command the first device to operate at a predetermined percentage of maximum power.
The system for monitoring power can further include a plurality of power monitoring devices, each located in the power distribution system to measure at least one characteristic of power provided to a respective branch of the power distribution system, and each having an output to couple to the controller to provide a value of the characteristic measured. Each of the respective branches of the power distribution system can provide power to at least one respective device, and the controller can be adapted to send a power signal to each respective device to command each device to operate at the predetermined percentage of maximum power. The controller can be adapted to send the power signal to devices powered by one branch at a same time, to cause each of the devices on the one branch to operate at the predetermined percentage of maximum power. The controller can be adapted to total the values measured for each of a plurality of branch circuits and compare the total with a first overload value to detect an overload condition. The controller can be adapted to send an alarm signal to an operator upon detection of an overload condition. The controller can be adapted to send a signal to disconnect power to one or more devices upon detection of an overload condition. The at least one characteristic can be electrical current.
The controller of the power monitoring system can further include a first network interface to communicate with devices powered by the power distribution system over a first communications network and a second network interface to communicate over a second communications network. Each of the plurality of power monitoring devices can include a network interface to communicate with the controller over the second communications network. The power distribution system can include an uninterruptible power supply, and the controller can be adapted to communicate with the uninterruptible power supply to detect that the uninterruptible power supply is operating on battery mode and replace the first overload value with a second overload value. The controller can be adapted to send a signal to interrupt power to at least one device upon detection that the uninterruptible power supply is operating on battery mode. The system can further include a plurality of temperature sensors that monitor temperature at locations within a facility, each of the temperature sensors having an output to communicate a temperature value to the controller. The controller can be adapted to compare temperature values received from the temperature sensors with predetermined values to detect an over temperature error condition, and upon detection of an over temperature error condition send an alarm signal. The controller can be adapted to send a signal to interrupt power to at least one device upon detection of an over temperature error condition. The predetermined percentage of maximum power can be 100 percent.
Another aspect of the present invention is directed to a method for monitoring and controlling a power distribution system that has a plurality of circuit branches for providing power to a plurality of devices. The method includes controlling a first device on a first circuit branch to operate at a predetermined percentage of maximum power, detecting a first value for a characteristic of power provided to the first circuit branch, controlling a second device on a second circuit branch to operate at a predetermined percentage of maximum power, detecting a second value for a characteristic of power provided to the second circuit branch, adding the first value to the second value to obtain a total value, comparing the total value to an overload value to detect an overload condition, and indicating an alarm condition when the total value exceeds the overload value.
The first device can be controlled to operate at less than the predetermined percentage of maximum power when the second device is controlled to operate at the predetermined percentage of maximum power. The method can further include controlling one of the plurality of devices to operate in a reduced power mode upon detection of an overload condition. The method can further include interrupting power to one of the plurality of devices upon detection of an overload condition. The characteristic measured can be electrical current. The method can further include communicating with the first device and the second device over a first communications network, and communicating with power detection devices over a second communications network. The power distribution system can further include an uninterruptible power supply, and the method can further include detecting when the uninterruptible power supply is operating in a battery mode, and controlling at least one of the plurality of devices to operate in a reduced power mode upon detection of the battery mode. The method can further include interrupting power to at least one of the plurality of devices upon detection of the battery mode. The power distribution system can be at least partially contained within a facility, and the method can further include measuring air temperature at a plurality of locations within the facility, comparing at least one value of air temperature measured with a predetermined value to detect an over temperature condition, and controlling at least one of the plurality of devices to operate in a reduced power mode upon detection of the over temperature condition. The predetermined percentage of maximum power can be 100 percent.
Yet another aspect of the present invention is directed to a system for monitoring and controlling a power distribution system that has a plurality of circuit branches for providing power to a plurality of devices. The system includes means for controlling each of the plurality of devices to operate at a predetermined percentage of maximum power, and means for detecting a value of a characteristic of power provided to each of the plurality of circuit branches.
The system can further include means for comparing a total value of the characteristic with a predefined value to detect an overload condition. The system can further include means for interrupting power to at least one of the plurality of devices when an overload condition is detected. The characteristic can be electrical current. The power distribution system can include at least one uninterruptible power supply, and the system can further include means for detecting that the uninterruptible power supply is in a battery mode of operation, and means for adjusting the predefined value when the uninterruptible power supply is in the battery mode of operation. The system can further include means for detecting air temperature values in a facility containing the power distribution system. The system can further include means for comparing the detected air temperature values with predetermined temperature values, and means for interrupting power to at least one of the plurality of devices when the detected air temperature values exceed the predetermined temperature values. The predetermined percentage of power can be 100 percent.